The steady increase in volume of data transfer will ultimately lead to a need for a radically new approach to telecommunication. Incremental approaches in electronic speeds are reaching the physical limits of what is possible. With optical pulses of a few tens of femtoseconds that are routinely produced, digital communication could in principle reach a rate of tens of THz. The fundamental difficulty in exploiting the high potential data rate of femtosecond optical pulses is that the original signal to be transmitted is at a much slower clock rate, in the GHz rather than THz range.
One approach being taken in telecommunications is wavelength multiplexing. Ten or twenty signals are broadcast simultaneously at neighboring wavelength. There are fundamental limitations for laser communication through wavelength multiplexing. One is that it is still the electronics that determines the speed at which each channel is broadcast. Hence, it is not possible to exploit the fs capability of optics. Additionally, the number of channels is limited by the bandwidth of the emitting/amplifying laser medium. It is simply the ratio of the laser bandwidth to the bandwidth of each channel. The shorter the pulse, the smaller the number of channels available. What is needed is improved methods and apparatus for providing high speed communications.